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Abstract

Direct to home (DTH) television is a wireless system for delivering television programs directly to the viewer's house. In DTH television, the broadcast signals are transmitted from satellites orbiting the Earth to the viewer's house. Each satellite is located approximately 35,700 km above the Earth in geosynchronous orbit. These satellites receive the signals from the broadcast stations located on Earth and rebroadcast them to the Earth. The viewer's dish picks up the signal from the satellite and passes it on to the receiver located inside the viewer's house. The receiver processes the signal and passes it on to the television.

Description of Direct to Home Television


The DTH provides more than 200 television channels with excellent quality of reception along with teleshopping, fax and internet facilities. DTH television is used in millions of homes across United States, Europe and South East Asia. Direct to home television is a wireless system for delivering television programming directly to a viewer's house. Usually broadcasting stations use a powerful antenna to transmit radio waves to the surrounding area.

Viewer's can pickup the signal with a much smaller antenna. The main limitation of broadcast television is range. The radio signal used to broadcast television shoot out from the broadcast antenna in a straight line. Inorder to receive these signals, you have to be in the direct "line of sight" of the antenna. Small obstacles like trees or small buildings aren't a problem; but a big obstacle, such as Earth, will reflect these waves.

If the Earth were perfectly flat, you could pickup broadcast television thousands of miles from the source. But because the planet is curved, it eventually breaks the signal's line of sight. The other problem with broadcast television is that the signal is often distorted even in the viewing area. To get a perfectly clear signal like you find on the cable one has to be pretty close to the broadcast antenna without too many obstacles in the way.

Uplinking is usually done in the Ka band (26-40 GHz). The satellites are in geosynchronous orbit about 35,700 km above the equator. Six to seven channels per transponder at 4 - 6 Mbps bit rate can be offered because of digital compression techniques. The bit rate is reduced from 216 Mbps to about 8 Mbps by eliminating redundant information. Thus a satellite with 30 transponders can broadcast about 210 channels(30 X 7) with excellent audio and video quality.

When satellite transmission is aimed at individual home users the radiated power from the satellite is directed not to an individual receiving antenna but to a specific area known as coverage zone. Contour maps are used to represent the distribution of radiated power of the satellite, with each satellite beam forming its own footprints across the globe.